Pyrite discs in coal: evidence for fossilized bacterial colonies

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Discs of pyrite from 1 to 3 mm in diameter and ∼100 μm thick were observed within fracture planes in coal from the Black Mesa coal deposit in northeastern Arizona. The pyrite discs were composed of aggregates of crystals, which suggested that sulfide mineral diagenesis had initiated at multiple nucleation sites and occurred prior to the compaction forces occurring during coal formation. Stable sulfur isotope analysis of the discs (δ34S = −31.7‰) supports a bacterial origin resulting from dissimilatory sulfate reduction. Fossilized bacteria on the disc surfaces (average = 27/100 μm2) appeared as halos when viewed using reflected light microscopy, but were lenticular by scanning electron microscopy, each microfossil being 2–3 μm in length. A fossilized bacterial colony (pyrite disc), 1 mm in diameter, would contain ∼2.1 × 107 microfossils. These microfossils were not observed on hydrothermal pyrite. Coating and in-filling of sulfate-reducing bacteria with iron disulfide during in vitro sulfide mineral diagenesis provide mechanisms to explain the preservation of the three-dimensional lenticular microfossils observed on the pyrite discs.
Publication type Article
Publication Subtype Journal Article
Title Pyrite discs in coal: evidence for fossilized bacterial colonies
Series title Geology
DOI 10.1130/0091-7613(2001)029<0047:PDICEF>2.0.CO;2
Volume 29
Issue 1
Year Published 2001
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geology
First page 47
Last page 50
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